Pulse signal amplifier

ABSTRACT

A pulse signal amplifier is disclosed which includes at least an emitter follower type drive stage consisting of a pair of complementary transistors and a field effect transistor connected to the drive stage and ON/OFF controlled thereby. A capacitive element is connected between the collectors of the complementary transistors and a pulse current signal source is provided to supply a charge current to the capacitive element and a drive current to the complementary transistors.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a pulse signal amplifier, andis directed more particularly to a pulse signal amplifier in which apower supply circuit for a drive stage is simplified.

2. Description of the Prior Art

In a prior art pulse signal amplifier having an FET (field effecttransistor) as the final stage amplifying element, in order to drive theFET at a high speed there is provided a drive circuit which consists ofa pair of complementary transistors connected in an emitter-followerconfiguration. In this case, a power supply circuit for the drivecircuit is provided separately from a power supply circuit to the finalstage amplifying element so as to avoid that the fluctuation in thepower supply source at the final stage affects on the drive stage.

However, when the power supply circuits are provided separately for thefinal stage and the drive stage as in the prior art, the circuitconstruction becomes complicated and the circuit becomes expensive.

OBJECTS AND SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a pulsesignal amplifier free from the defect inherent to the prior art.

It is another object of the invention to provide a pulse signalamplifier in which a part of a pulse current signal driving a drivingcircuit is charged in a capacitor and the voltage thereacross is used asa DC voltage source for the drive stage.

In accordance with an aspect of the present invention, a pulse signalamplifier is provided, which includes a pulse current signal source, animpedance transfer circuit consisting of first and second transistorseach having first, second and third electrodes, the first electrodes ofwhich are connected to each other and supplied with the output of thepulse current signal source and the second electrodes of which areconnected to each other, a field effect transistor having gate, sourceand drain electrodes, the gate electrode of which is connected to theconnection point of the second electrodes of said first and secondtransistors, the drain and source electrodes of which are connectedbetween a DC voltage source and a reference point through a load, thepulse signal amplifier being characterized by a capacitive elementhaving a pair of first and second terminals, the first terminal of whichis connected to the third electrode of the first transistor and thesecond electrode of which is connected to the third electrode of thesecond transistor and to the reference point, and a switching elementconnected between the output of the pulse current signal source and thethird electrode of the first transistor so as to carry a part of theoutput current of the pulse current signal source to the capacitiveelement to charge the same when the gate current of the field effecttransistor is not supplied through the third and second electrodes ofthe first transistor.

The other objects, features and advantages of the present invention willbecome apparent from the following description taken in conjunction withthe accompanying drawings through which the like reference numerals andletters designate the same elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a prior art pulse signal amplifier;

FIG. 2 is a circuit diagram showing an example of the pulse signalamplifier according to the present invention;

FIGS. 3A to 3D are waveform diagrams used for explaining an operation ofthe pulse signal amplifier of the invention shown in FIG. 2; and

FIG. 4 is a circuit diagram showing another example of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to better understand the present invention, a prior art pulsesignal amplifier will be described firstly with reference to FIG. 1. Inthis prior art amplifier by way of example, there is provided aninsulating gate type field effect transistor Q_(1a) (in this example, anN-channel enhancement type MOS FET (field effect transistor) which formsan amplifier of a common source circuit type. A source of the transistorQ_(1a) is grounded and its drain is connected to a voltage source +Bthrough a load registor R_(2a) and to an output terminal t.

There is also provided an impedance transfer circuit 3a consisting oftransistors. In this case, the impedance transfer circuit 3a is formedof an emitter-follower configulation type complementary push-pullcircuit using bi-polar transistors Q_(2a) (PNP-type) and Q_(3a)(NPN-type). In this case, in place of the bi-polar transistor an FET canbe used. This impedance transfer circuit 3a is supplied with anoperating voltage from a DC voltage source E_(a). In detail, thecollector of the transistor Q_(3a) is connected to the positive terminalof the voltage source E_(a) which is grounded at its negative terminal.The emitter of the transistor Q_(3a) is connected to the emitter of thetransistor Q_(2a) whose collector is grounded. The output side of theimpedance transfer circuit 3a i.e. connection point between the emittersof the transistors Q_(2a) and Q_(3a) is connected to the gate of thetransistor Q_(1a).

There is further provided a pulse current signal source 2a formed ofPNP-type bi-polar transistor Q_(4a) whose emitter is connected through aresistor R₂ to the voltage source +B and of a pulse source 1 which isconnected at its one end to the base of the transistor Q_(4a) and at itsother end to the voltage source +B. The collector of the transistorQ_(4a) in the pulse current signal source 2a is grounded through aresistor R_(1a) and also commonly connected to the bases of thetransistors Q_(2a) and Q_(3a) in the impedance transfer circuit 3a.

In the above prior art pulse signal amplifier, the DC voltage sourceE_(a), which supplies the DC voltage to the impedance transfer circuit3a as the operating voltage, is separate from the voltage source +B forthe transistor Q_(1a), so that this prior art pulse signal amplifier iscomplicated in circuit construction and hence expensive.

Now, the present invention free from the defect of the prior art will behereinafter described with reference to the attached drawings.

An example of the pulse signal amplifier according to the presentinvention will be described with reference to FIG. 2 in which thereference numerals corresponding to those used in FIG. 1 designate thesame elements, respectively, and their detailed description will beomitted.

In the example of the invention shown in FIG. 2, a voltage sourcecircuit 4a, which is a parallel circuit consisting of a capacitor C_(a)(for example, having the capacity of 10 μF) and a Zener diode D_(za) asa constant voltage element, is connected to the pulse current signalsouce 2a in the pulse signal amplifier in place of the voltage sourceE_(a) used in the piror art, and the output from the voltage sourcecircuit 4a is applied to the impedance transfer circuit 3a as theoperating voltage. That is, the collector of the transistor Q_(3a) isgrounded through the capacitor C_(a) and connected to the cathode of theZener diode D_(za) whose anode is in turn grounded. The collector of thetransistor Q_(3a) is also connected to that of the transistor Q_(4a)through a diode D_(2a).

An operation of the pulse signal amplifier of the invention shown inFIG. 2 will be described with reference to the waveforms illustrated inFIGS. 3A to 3D. A pulse current or rectangular current I₁, which isdeveloped from the pulse current signal source 2a and has the waveformshown in FIG. 3A and the frequency of, for example, 500 KH_(z), isdivided into a current I₂, which flows to the resistor R_(1a) and to thebases of the transistors Q_(2a) and Q_(3a) and whose waveform is shownin FIG. 3B, and into a current I₃, which flows through the diode D_(2a)to the voltage source circuit 4a mainly and whose waveform is shown inFIG. 3C. A current I_(G) flowing to the gate G of the transistor Q_(1a)has such a waveform as just formed by differentiating the rectangularcurrent I₁ shown in FIG. 3A, as illustrated in FIG. 3D. This is causedby the input capacities (of for example, about 1000 pF) existing betweenthe gate and drain and between the gate and source of the transistorQ_(1a). Since the current I_(G) has the above waveform, the waveforms ofthe current I₂ and I₃ are not rectangular as that of the current I₁ butof waveforms such as shown in FIGS. 3B and 3C, respectively. The valueof the current I₂ at its flat portion is expressed by (V_(x)+V_(d))/R_(1a) if it is assumed that the DC voltage of the voltagesource circuit 4a is taken as V_(x), the forward voltage drop of thediode D_(2a) is taken as V_(d), and the resistance of the resistorR_(1a) is taken as R_(1a), respectively.

Therefore, when the transistor Q_(4a) is in ON-state and the transistorQ_(3a) is in OFF-state or period T_(c) in FIG. 3D, the capacitor C_(a)is charged by the current I₃ (=I₁ -I₂). The voltage across the capacitorC_(a) can be used as the voltage source of the impedance transfercircuit 3a. In this case, if the mean value of a partial current of thecurrent I₃, which is used to charge the capacitor C_(a), is selectedgreater than the mean value of the positive portion of the currentI_(G), the potential at the collector of the transistor Q_(3a) can bekept substantially constant. In the example of the invention shown inFIG. 2, the Zener diode D_(za) is provided so as to prevent the voltageacross the capacitor C_(a) from being increased unnecessarily.

Thus, the field effect transistor Q_(1a) is turned ON and OFF inresponse to the polarity of the pulse source 1 of the pulse currentsignal source 2a, and an amplified output pulse is delivered to theoutput terminal t.

In the example of the invention shown in FIG. 2, the enhancement typeMOS FET is used as the FET Q_(1a), but in place thereof a depressiontype MOS FET or triode characteristic FET can be used.

Another example of the invention will be now described with reference toFIG. 4, in which the parts or elements corresponding to those in FIG. 2are marked with the same reference numerals and letters and theirdetailed description will be omitted.

The example of the invention shown in FIG. 4 is the case where thepresent invention is applied to a complementary push-pull type MOS FETpulse signal amplifier so that two amplifier circuits each beingsubstantially same as that shown in FIG. 2 are used. In this case, a PWM(pulse width modulated) signal source is used as the pulse signalsource.

In FIG. 4, transistors Q_(1a) and Q_(1b) are respectively insulatinggate typefield effect transistors of an N-channel and a P-channel types(in the illustrated example, enhancement type MOS FETs) and the MOS FETsare each connected in a common source configuration circuit. That is,the sources of the respective transistors Q_(1a) and Q_(1b) areconnected to the voltage sources -B and +B and the drains thereof areconnected together to the output terminal t to which a load 6 isconnected.

The impedance transfer circuit 3a and the voltage source circuit 4a forthe transistor Q_(1a) are formed similar to those of FIG. 2. In thiscase, in place of the resistor R_(1a) used in FIG. 2, an SRPP (shuntregulated push-pull) circuit 5a is provided as an active load which willbe described later. That is, the SRPP circuit 5a is formed of a PNP-typebi-polar transistor Q_(5a), a diode D_(1a) connected between the baseand emitter of the transistor Q_(5a) and a resistor R_(3a) connectedbetween the base and collector of the transistor Q_(5a). The base of thetransistor Q_(5a) is further connected to the collector of thetransistor Q_(4a), the collector of the transistor Q_(5a) is connectedto the voltage source -B and the emitter thereof is connected to thecommonly connected bases of the transistors Q_(2a) and Q_(3a),respectively.

Since the pulse current signal source, the impedance transfer circuit,the voltage source circuit and the SRPP circuit for the other transistorQ_(1b) are substantially same as those for the transistor Q_(1a), theyare marked with the corresponding reference with the suffix b in placeof a and their detailed description will be omitted. In this case, theconductivity and the connection polarity of the transistors and theconnection polarity of the diodes in the two amplifier circuits areselected opposite. The pulse source 1 (which is such a pulse source,whose pulse width is to be modulated and which has the carrier frequencyof, for example, 500 KH_(z)) is connected between the commonly connectedbases of the transistors Q_(4a) and Q_(4b) and the ground.

In the example of FIG. 4, it is possible that, at the base side of thetransistors Q_(3a) and Q_(2a) and similarly at the base side of thetransistors Q_(3b) and Q_(2b), there is additionally provided a diode inthe same direction as the diode D_(1a) and diode D_(1b), respectively.

Next, an operation of the example of the invention shown in FIG. 4 willbe now described. During the negative half cycle of the pulse source 1,the transistor Q_(4a) turns ON and hence the current I₁ flows out fromthe collector of the transistor Q_(4a). This current I₁ is divided intothe current I₃ to the diode D_(2a) and the current I₂ to the resistorR_(3a) as set forth above. A part of the current I₂ flows through thediode D_(1a) to the base of the transistor Q_(3a) in the impedancetransfer circuit 3a, so that the transistor Q_(3a) becomes ON. When thediode D_(1a) becomes ON, the base-emitter of the transistor Q_(5a),which forms the SRPP circuit 5a together with the diode D_(1a) and theresistor R_(3a), is reverse-biased and hence the transistor Q_(5a) turnsOFF. Due to the conduction of the transistor Q_(3a), the input capacityof the FET Q_(1a) is charged by the current I_(G) (its positive portion)shown in FIG. 3D and then the FET Q_(1a) turns ON. Thus, at the outputterminal t there is developed the voltage -B. In this case, during theinterval T_(c) shown in FIG. 3D, the capacitor C_(a) is charged by thecurrent I₃, and accordingly it serves as the voltage source for theimpedance transfer circuit 3a.

When the transistor Q_(4a) is in OFF-state, the base-emitter of thetransistor Q_(5a) is biased in the forward direction and hence thetransistor Q_(5a) turns ON (diode D_(1a) turns OFF). Thus, at this timethe transistor Q_(2a) is made ON, so that the input capacity of the FETQ_(1a) is discharged and hence the FET Q_(1a) becomes OFF.

During the positive half cycle of the pulse source 1, the similaroperation to that described above is carried out by the other amplifiercircuit and hence the other FET Q_(1b) turns ON with the result that atthe output terminal t there is developed the voltage +B.

According to the present invention, the output side of the impedancetransfer circuit, which consists of transistors, is connected to thegate of the insulating gate type FET, which forms the common sourceconfiguration type amplifier, and the pulse current signal source isconnected to the input side of the impedance transfer circuit. Thus, inthe invention there is no need to provide a separate voltage source tothe impedance transfer circuit from the FET. As a result, the pulsesignal amplifier of the present invention is simple in circuitconstruction and inexpensive.

It will be apparent that many modifications and variations could beeffected by one skilled in the art without departing from the spirits orscope of the novel concepts of the present invention so that the spiritsor scope of the invention should be determined by the appended claimsonly.

I claim as my invention:
 1. A pulse signal amplifier comprising pulsecurrent signal source; an impedance transfer circuit consisting of firstand second transistors each having first, second and third electrodes,the first electrodes of which are connected to each other and suppliedwith the output of said pulse current signal source and secondelectrodes of which are connected to each other; a field effecttransistor having gate, source and drain electrodes, the gate electrodeof which is connected to the connection point of the second electrodesof said first and second transistors, the drain and source electrodes ofwhich are connected between a DC voltage source and a reference pointthrough a load, said pulse signal amplifier is characterized by:(a) acapacitor having a pair of first and second terminals, the firstterminal of which is connected to the third electrode of said firsttransistor and the second terminal of which is connected to the thirdelectrode of said second transistor and to said reference point; and (b)a diode connected between the output of said pulse current signal sourceand the third electrode of said first transistor so as to carry a partof the output current of said pulse current signal source to saidcapacitor to charge the same when the gate current of said field effecttransistor is not supplied through the third and second electrodes ofsaid first transistor.
 2. A pulse signal amplifier according to claim 1,further including constant voltage means having first and secondterminals connected across said capacitor.
 3. A pulse signal amplifieraccording to claim 2, in which said first and second transistors are ofan NPN conductive type and of a PNP conductive type, respectively, thefirst and second transistors being connected in common collectorconfiguration and said field effect transistor comprises an N-channelenhancement type MOS field effect transistor connected in common sourceconfigulation.
 4. A pulse signal amplifier according to claim 3, inwhich said pulse current signal source comprises a third transistorhaving base, emitter and collector electrodes, the collector electrodeof which is used for the output of said pulse current signal source andthe base-emitter circuit of which is supplied with a pulse signal to beamplified so as to ON/OFF control the same.
 5. A pulse signal amplifiercomprising a pulse current signal source; a first impedance transfercircuit consisting of first and second transistors each having first,second and third electrodes, the first electrodes of which are connectedto each other and supplied with the output of said pulse current signalsource and second electrodes of which are connected to each other; afirst field effect transistor having gate, source and drain electrodes,the gate electrode of which is connected to the connection point of thesecond electrodes of said first and second transistors, the drain andsource electrodes of which are connected between a first DC voltagesource and a reference point through a load; a second impedance transfercircuit consisting of third and fourth transistors each having first,second and third electrodes, the first electrodes of which are connectedto each other and supplied with the output of said pulse current signalsource and second electrodes of which are connected to each other; asecond field effect transistor having gate, source and drain electrodesthe gate electrode of which is connected to the connection point of thesecond electrodes of said third and fourth transistors, and the drainand source electrodes of which are connected between a second DC voltagesource and said reference point through said load, said pulse signalamplifier is characterized by:(a) a first capacitor having a pair offirst and second terminals, the first terminal of which is connected tothe third electrode of said first transistor and the second terminal ofwhich is connected to the third electrode of said second transistor andsaid first DC voltage source; (b) a first diode connected between theoutput of said pulse current signal source and the third electrode ofsaid first transistor so as to carry a part of the output current ofsaid pulse current signal source to said first capacitor to charge thesame when the gate current of said first field effect transistor is notsupplied through the third and second electrodes of said firsttransistor; (c) a second capacitor having a pair of first and secondterminals, the first terminal of which is connected to the thirdelectrode of said third transistor and to said second DC voltage sourceand the second terminal of which is connected to the third electrode ofsaid fourth transistor; and (d) a second diode connected between theoutput of said pulse current signal source and the third electrode ofsaid fourth transistor so as to carry a part of the output current ofsaid pulse current signal source to said second capacitor to charge thesame when the gate current of said second field effect transistor is notsupplied through the third and second electrodes of said fourthtransistor.
 6. A pulse signal amplifier according to claim 5, furtherincluding(a) first constant voltage means having a pair of terminalsconnected across said first capacitor means; and (b) second constantvoltage means having a pair of terminals connected across said secondcapacitor means.
 7. A pulse signal amplifier according to claim 6, inwhich said first and second transistors are of an NPN conductive typeand of a PNP conductive type, respectively, the first and secondtransistors being connected in common collector configuration,respectively and said first field effect transistor comprises anN-channel enhancement type MOS field effect transistors connected incommon source configuration, and in whichsaid third and fourthtransistors are of an NPN conductive type and a PNP conductive type,respectively and being connected in common collector configuration,respectively, and said second field effect transistor comprises aP-channel enhancement type MOS field effect transistor connected incommon source configuration.
 8. A pulse signal amplifier according toclaim 5, further including first and second drive circuits connectedbetween the output of said pulse current signal source and the inputs ofsaid first and second impedance transfer means, respectively, so as todrive the same.
 9. A pulse signal amplifier according to claim 8, inwhich each of said first and second drive circuit comprises a furtherdiode and a further transistor.
 10. A pulse signal amplifier accordingto claim 5, in which said pulse current signal source comprises a pairof transistors each connected in common emitter configuration and ON/OFFcontrolled in response to a pulse signal supplied to the inputelectrodes thereof.